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AQA A Level Chemistry

3.3.4
Alkenes

AQA 3.3.4 covers the structure and bonding of alkenes, electrophilic addition with HBr, H2SO4 and Br2, the bromine test for unsaturation, major and minor products, and addition polymers including PVC and plasticisers. E-Z isomerism from 3.3.1.3 is revised alongside it.

Exam Paper
Paper 2
7405/2
Specification Points
3.3.4.1 – 3.3.4.3
plus 3.3.1.3 E-Z isomerism
Topic Parts
5 parts
Revision notes available
Exam Board
AQA
AQA 7405

Revision Notes

Work through each part of AQA 3.3.4 in a structured sequence.

σ and π bonds
Alkene
Bonding
1

Alkene Bonding

Unsaturated hydrocarbons, the double covalent bond as a centre of high electron density, and why alkenes react.

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Stereoisomers
E-Z
Isomerism
2

E-Z Isomerism

Restricted rotation about the C=C bond, the conditions for E-Z isomerism and the Cahn-Ingold-Prelog rules (3.3.1.3).

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Curly arrows
Electrophilic
Addition
3

Electrophilic Addition Mechanism

The mechanism with HBr, H2SO4 and Br2, carbocation intermediates and heterolytic fission.

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Addition reactions
Reactions of
Alkenes
4

Reactions of Alkenes

Halogens, hydrogen halides, concentrated sulfuric acid, the bromine water test and hydration with steam.

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Poly(alkenes)
Addition
Polymers
5

Addition Polymers

Addition polymerisation, repeating units, monomers and the IUPAC names of addition polymers.

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PVC and plasticisers
Polymer
Properties
6

Polymer Properties and PVC

Why addition polymers are unreactive, the intermolecular forces between chains, and how plasticisers modify PVC.

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Specification Coverage

3.3.4 Alkenes – AQA A Level Chemistry

The following AQA specification points outline the knowledge and skills students are expected to demonstrate for Alkenes, together with the E-Z isomerism content from 3.3.1.3 that is assessed with them.

3.3.4 Alkenes

3.3.4.1
Structure, bonding and reactivity
Alkenes are unsaturated hydrocarbons.
Bonding in alkenes involves a double covalent bond, a centre of high electron density.
3.3.4.2
Addition reactions of alkenes
Electrophilic addition reactions of alkenes with HBr, H2SO4 and Br2.
The use of bromine to test for unsaturation.
The formation of major and minor products in addition reactions of unsymmetrical alkenes.
Students should be able to:
1
outline the mechanisms for these reactions
2
explain the formation of major and minor products by reference to the relative stabilities of primary, secondary and tertiary carbocation intermediates.
3.3.4.3
Addition polymers
Addition polymers are formed from alkenes and substituted alkenes.
The repeating unit of addition polymers.
IUPAC rules for naming addition polymers.
Addition polymers are unreactive.
Appreciate that knowledge and understanding of the production and properties of polymers has developed over time.
Typical uses of poly(chloroethene), commonly known as PVC, and how its properties can be modified using a plasticiser.
Students should be able to:
1
draw the repeating unit from a monomer structure
2
draw the repeating unit from a section of the polymer chain
3
draw the structure of the monomer from a section of the polymer
4
explain why addition polymers are unreactive
5
explain the nature of intermolecular forces between molecules of polyalkenes.

3.3.1.3 Isomerism

3.3.1.3
Isomerism (E-Z stereoisomerism)
Stereoisomers have the same structural formula but the bonds are arranged differently in space.
E-Z isomerism is one form of stereoisomerism and occurs as a result of restricted rotation about the planar carbon-carbon double bond.
Cahn-Ingold-Prelog (CIP) priority rules.
Students should be able to:
1
draw the structural formulas of E and Z isomers
2
apply the CIP priority rules to E and Z isomers.